The present invention relates to an improved vinyl chloride polymer having excellent processability and physical properties, and more particularly to a particulate vinyl chloride polymer composition having improved flowability and heat stability and capable of providing moldings having excellent heat resistance, rigidity and impact resistance, and a process for the preparation thereof.
Polyvinyl chloride has excellent chemical and mechanical properties and is inexpensive, and therefore it has been employed industrially in large quantities. However, since the polyvinyl chloride is poor in processability and heat stability, and since the processing temperature is close to the thermal decomposition temperature, it is difficult to adopt a manner such as lowering a melt viscosity of the polymer at high temperatures like ordinary resins and the polyvinyl chloride has had to be processed in the state that the flowability is low. In particular, in case of admixing the polyvinyl chloride with large quantities of an inorganic filler for imparting the rigidity and heat resistance to the obtained moldings or for cost down, the processability and heat stability are remarkably lowered and the molding becomes impossible.
It is known to use a polyvinyl chloride having a low degree of polymerization in order to improve the molding processability, especially flowability. However, a polyvinyl chloride having a low degree of polymerization has the defects that not only it is poor in heat stability, but also it causes the lowering of impact resistance and tensile strength. Also, in order to improve the molding processability, it is proposed to copolymerize vinyl chloride with a comonomer such as an alkyl acrylate or an alkyl vinyl ether. However, such a vinyl chloride copolymer has the defect that the heat stability of the polymer or the heat resistance and tensile strength of the obtained moldings are lowered, though the melt viscosity is lowered by the copolymerization of the comonomer and whereby the flowability is improved. Besides, it is known to add a plasticizer and a lubricant to polyvinyl chloride for improving the molding processability. However, the addition thereof in large quantities is required in obtaining a sufficient flowability, and it causes problems that the heat resistance and rigidity are lowered, gelation is ununiform or insufficient and bleeding takes place.